Film sprocket



April 25, 1939- J. M. WEHNER 2,155,518

FILM SPROCKET Filed Jan. 29, 1957 VII] 16; &

\ 3nnentor 13 John M. Vl ehner I attorney Patented Apr. 25, 1939 PATENT OFFICE FILM SPROCKET' John M. Wehner, Audubon, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 29, 1937, Serial No. 122,941

8 Claims.

This invention relates to new and improved sprockets, and more particularly to the type of sprockets used for feeding perforated motion picture film.

Film sprockets, as constructed according to the prior art, were customarily turned from a solid bar of stock and the teeth were thereafter milled. In the course of milling of the teeth, and in order to secure a proper contour to the faces thereof contacting with the edges of the perforation in the film, it was necessary for the milling cutter to pass below the surface of the sprocket drum adjacent to the teeth, thereby leaving objectionable sharp edges adjacent the teeth. In attempting to avoid these objectionable sharp edges, which tended to cut the film at the corners of the sprocket holes and thereby cause film breakage, various schemes have been resorted to, none of which have been found entirely satisfactory.

The purpose of my invention is to provide a sprocket wherein the surface of the sprocket drum is perfectly smooth and free from irregularities while the teeth may be made to any desired degree of precision and inserted in the said drum as a unit. This is accomplished by making the drum of the sprocket integral with the hub and turned smooth on the outside to the requisite degree of precision. This drum is then slotted longitudinally and the tooth unit is inserted therein with the teeth projecting above the slots the required amount, and the remainder of each slot is then fitted in so as to be smooth with the surface of the drum by means of a second member provided with radial extensions adapted to fit the slots.

One object of the invention is to provide a sprocket which will be free of irregularities which might tend to damage the film.

Another object of my invention is to provide a sprocket which may be made to a high degree of precision.

Another object of my invention is to provide a sprocket which may be readily fabricated by simple machinery.

Another object of my invention is to provide a sprocket wherein the sprocket teeth and the sprocket drum may be made of different materials particularly adapted to the specific purposes.

Other and incidental objects of my invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing, in 55 which:

Figure 1 is an end view of my improved sprocket.

Figure 2 is a longitudinal section of my improved sprocket showing a form thereof adapted for use with standard 16 mm. film, and

Figure 3 is an exploded longitudinal section of my sprocket.

As shown in the several figures of the drawing, the sprocket comprises a body member Ill having at its end drum members II and I2, these three portions of the sprocket being preferably formed from a single piece of material, although they may be fabricated from a plurality of parts if so desired.

Since, in the form of the invention shown, the sprocket is intended to operate with 16 mm. film, which has sprocket holes only along one edge, sprocket teeth are shown only at the corresponding end of the sprocket. It will be apparent, however, that the sprocket may be made in any size desired and sprocket teeth may be provided at both ends of the sprocket if so desired, as, for example, to operate with standard mm. film.

The drum I2 is slotted longitudinally as shown at l 3, so as to provide room for the sprocket teeth to be inserted in the slots with a snug fit. An annular member 14, which has a circumference of such diameter as to fit snugly within the drum I2, is provided. Teeth I5 extend from this circumference and are so shaped that they extend with parallel sides through the slots 13 to the surface of the drum l2, completely filling the slots in the circumferential direction, and fitting snugly against the bottom of the slots. The teeth are so shaped as to have the proper contour above the surface of the drum [2. It will be apparent that any diametrically opposed pair of teeth [5 will, by reason of the snug fit in the corresponding slots l3, definitely determine the extended position of the pair of teeth located at 90 to this diameter. For this reason the external diameter of the member l4 may vary within wide limits without affecting the accuracy of the positioning of the teeth.

This annular member l4 may be made of any desired material, as, for example, a steel which may be shaped and then hardened and ground to finished dimensions, whereas the members II], II and I2 may be made of a somewhat softer grade of steel in order to machine readily to the required degree of precision.

A second annular member l6 may be provided, if desired, which, like the member l4, has a circumference adapted to fit within the drum I 2. Extending beyond this circumference are the projections H, which, like the bases of the teeth I5, are made with parallel sides of such dimensions as to fit snugly into the slots I3. The outer surfaces of the projections H are turned to the same radius as the outer surface of the drum I2, and therefore serve to fill the slots I3 both circumferentially and radially, so as to render the true surface of the composite member, including the members I2, I4 and I6, perfectly smooth. The member I6 is, further, made of such thickness as to just fill the portion of the depth of the drum I2 which remains after the insertion of the member I4. When the member I4 is inserted into the member I2 with the teeth I5 projecting into the slots I3, and the member I6 is inserted into the member I2, with the projections II filling the slots I3, there is produced a sprocket which is perfectly smooth and uniform over the entire surface of the drum I2, with no apertures or extending members adjacent to the edges of sprocket I5. The member I6, however, is not essential and may be omitted.

The members I4 and I6 may be secured within the drum I2 either by making them of such dimensions as to be a press fit, by spinning down an edge of the drum I2 over the edge of the member I6, by soldering or riveting the elements together, or, preferably, by means of the screws I8 as indicated. The use of screws to secure these members together permits the members I6 and I4 to be removed and, in case of wear on the faces of sprocket I5, the member I4 may be replaced without replacement of the remainder of the sprocket.

I claim as my invention:

1. A sprocket of the class described comprising a cylindrical drum having longitudinal slots therein, an annular member fitting within said drum and having sprocket teeth thereon passing through said slots, and means for securing said members to said drum.

2. A sprocket of the class described comprising a cylindrical drum having longitudinal slots therein, and an annular member fitting within said drum and having sprocket teeth thereon passing through said slots, the base portions of said sprocket teeth completely filling said slots circumferentially.

3. A sprocket of the class described comprising a cylindrical drum having longitudinal slots therein, an annular member fitting within said drum and having sprocket teeth thereon passing through said slots, and a second annular member fitting within said drum and having projections thereon extending into and filling the portions of said slots adjacent to the said teeth.

4. A sprocket of the class described comprising a cylindrical drum having longitudinal slots therein, an annular member fitting within said drum and having sprocket teeth thereon passing through said slots, a second annular member fitting within said drum and having projections thereon extending into and filling the portions of said slots adjacent to the said teeth, and means for securing said members together.

5. A sprocket of the class described comprising a cylindrical drum having longitudinal slots therein, an annular member fitting within said drum and having sprocket teeth thereon passing through said slots, and a second annular member fitting within said drum and having projections thereon extending into and filling the portions of said slots adjacent to the said teeth, the base portions of said sprocket teeth completely filling said slots circumferentially.

6. A sprocket of the class described comprising a body member having a hollow cylindrical drum at its end, said drum being provided with longitudinal slots, and an annular member having a circumference of such diameter as to fit snugly within said drum, said member having sprocket teeth thereon passing through said slots.

'7. A sprocket of the class described comprising a body member having a hollow cylindrical drum at its end, said drum being provided with longitudinal slots, and an annular member having a circumference of such diameter as to fit snugly within said drum, said member having sprocket teeth thereon extending radially therefrom in the plane thereof, and said sprocket teeth passing through said slots.

8. The invention set forth in claim 7 characterized in that said sprocket teeth have parallel sides adjacent said circumference and having converging sides beyond said parallel sides, and characterized further in that said parallel sides extend through said slots to only the surface of said drum, said converging sides alone extending beyond said drum surface.

JOHN M. WEHNER. 

